The quaternary ammoniym salts of the elements of Group V of the Periodic System, are characterized by being, generally, very stable strong alkalis, which are highly ionized in aqueous solution in order to form stable cations containing the pentavalent element bound to the hydrocarboned sustituents by covalent bonds.
It is known that these quaternary salts are, in some cases, more reactive than the corresponding K or Na salts.
On the other hand, if the configuration and the organic chains of the quaternary salt are adequate, these compounds are easily soluble in organic solvents.
The capability of these quaternary salts to catalyze transfer reactions has been widely studied (Starks, Ch. M. and Liotta, CH. "Phase Transfer Catalysis". Academic Press (1978)).
In general, the phase transfer catalysis is carried out in a two-phase system, an organic phase and the other an aqueous or solid phase.
The reagent being present, for instance, in the aqueous phase, is transferred to the organic one, by the transfer catalyst, according to the schedule: ##STR2##
The reactions which can be carried out by this method are numerous and, as an example, the following can be cited: C-alkylizations, O-alkylizations, esterifications, halogen exchange, ester and chloride hydrolysis, carbene reactions and, in general, nucleophilic displacements of the kind: ##STR3## wherein Y can be for instance: Cl.sup.-, Br.sup.-, I.sup.-, --COO.sup.-, --NO.sub.2.sup.-, --NCO.sup.-, --OH.sup.-, --CN.sup.-, --SCN.sup.-.
A great number of these reactions are described by Keller, W. E. "Compendium of Phase-Transfer Reactions and Related Synthetic Methods", Fluka A. G. (1979).
The ammonium salt amount necessary to catalyze a reaction varies substantially depending on the type of reaction and the catalyst used. The reaction rate generally increases when the catalyst amount, the temperature or both, are increased.
In general, the catalyst amount used varies in the range between the 0.01% and the 50% by weight, with reference to the reagent in the least polar phase.
Besides ammonium salts, the following compounds may be used as phase transfer catalysts: phosphonium salts, crown ethers, microbicyclic compounds and polyethylene glycols.
Each one of them has specific disadvantages: quaternary salts usually have little stability, crown ethers and macrobicyclic compounds are expensive and toxic and polyethylene glycols are little effective.